The concept of Approach Lighting is quite simple. A signal remain dark (not illuminated) until a train approaches it (i.e. the block in advance of the signal is occupied). This has been primarily used in the western U.S. in remote locations where signal equipment operates on battery power. Having the signals unlit most of the time saves battery power as well as prolongs the life of the bulbs. The "rule" for illumination is simple: the signal shall be illuminated when the preceding block is occupied. The following sequence of events illustrates approach lighting as supported by our BlockMaster product.